The PMLN5277 has been discontinued.  The recommended replacement is the PMLN6854A;

Heavy Duty Headset with Noise Cancelling Boom Microphone, behind-the-head (can be worn with hardhat) - Noise Reduction Rating = 24dB

Compatible with: 

Motorola often changes the product SKU name. This product may have also been known as PMLN5277a, PMLN5277b, PMLN5277c, PMLN5277d, PMLN5277e, PMLN5277f, PMLN5277ar.